Study on the Soil Moisture Change During Continuous Drought in Winter of 2010 and Spring of 2011 in the Middle and Lower Reaches of Yangtze River

The variation tendency of soil water content and the relationship between soil drought and meteorological drought were analyzed based on the daily and the real-time observed data at Nanjing from July 2010 to June 2011,and the meteorological drought composite index and the soil relative humidity index were calculated by using meteorological observations at Nanjing and daily precipitation,10-100 cm soil moisture content at the experimental station constructed by Nanjing University of Information Science Technology and Institute of Arid Meteorology,CMA.The results show that Nanjing suffered a severe dry weather in winter of 2010 and spring of 2011,on November 5,2010,mild drought began to appear and changed to moderate drought on 12 Nov and severe drought on 28 Nov.,and then maintained at moderate and severe drought.Soil relative humidity reached moderate drought on 13 November,after 15 days of continuous severe meteorological drought,the soil moisture reached severe drought on 2 May,2011.The trends of meteorological and soil drought were basically consistent,but the extent of meteorological drought was more serious than that of soil drought,and the starting and ending time of soil drought lagged 1-3 days,and the drought development lagged behind more than 5 days.Weather and surface soil had higher sensitivity to precipitation,while the middle soil drought lasted long.In addition,when the meteorological drought duration reached 50-60 days,water would add from the deep layer to the top layer of soil.